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UNITED STATES PATENT OFFICEO NIELS G. SORENSEN, OF STOOKHOLM, SWEDEN, ASSIGNOR TO AKTIE BOLAGET URDA, OF SAME PLACE.

. METHOD OF DYEING LEATHER BLACK.

SPECIFICATION forming part of Letters Patent No. 243,000, dated June 14, 1 881.

Application filed October 26, 1880. (N0 specimens.) Patented in France October 11, 1880.

To all whom it may concern:

Be it known that I, NIELs GEORG SoREN- sEN, of Stockholm, in the Kingdom of Sweden, have invented a new and useful Method of Dyeing Leather Black, of which the following is a specification.

My invention relates to an improved method of dyeing leather black, by means of which such operation is eflectediu a more convenient, clean- 1y, efi'ectual, and durable manner than is the case when the ordinary methods are employed. The leather to which the said method of d yeing applies is such as has been tanned-that is to say, treated by or with and containing tannic acid, or gallic acid, or any of those derivations or combinations of or with such analogous acids as turn black when acted on by compounds or preparations of vanadium. The particular derivations or combinations of the said acids on which the compounds or preparations of vanadium have the desired efl'ect, and also the nature of the said compounds .or preparations which it is desirable to employ, are known to chemists. The dyeing can be effected at any time after the leather has been tanned, as abovereferred to. The action of the vanadic compound or preparation-which is employed in solutionon the surface or body of the leather treated is to turn it black. (The word black is not employed here in its strictly literal sense, but in its ordinary acceptation.)

It will be well understood that in order not to in any way injuriously aifect the quality of the leather it will be most advantageous to employ a neutralvanadic solution, and I have successfully employed a neutral solution of va nadiate of ammonia containing one per cent. of the latter salt. In order to bring out a full black colorI have found that the moderate use and application of heat is of beneficial influence.

The blackening ofleathcr by vanadium compounds or preparations, as hereinbefore described, is especially advantageous in the treatment of rnai'iufactured articles, such as boots and shoes, as the risk of damaging the upper portions of the same is avoided, and in the case of ornamental stitchingin saddlery-ware the leather is rendered black, while the Said stitching retains its proper color. It also allows of the operation to be performed without soiling the hands of the operator. Another advantage is that by the employment of vanadic compounds or preparations the color can be made to penetrate deeper into the leather than is the case with the ordinary dyes used. 

